1. Field
The presently disclosed subject matter relates to a projector type headlight, and particularly relates to a projector type headlight using a resin lens which can keep a grating shape and improve color bleeding in the vicinity of a boundary line between light and shade in a predetermined light distribution pattern, even when the diameter has been enlarged (to φ 60 mm or more, for instance).
2. Description of the Related Art
Conventionally, it has been known that in a headlight for vehicles (a so-called head lamp) that is configured so as to form a predetermined light distribution pattern including the boundary line between light and shade (referred to as a cutoff line as well) by the light which is emitted forward through a projection lens, like a projector type headlight or a direct projection type (direct type) headlight, color bleeding (referred to as color breakup as well) which originates in a chromatic aberration of the projection lens occurs in the vicinity of the boundary line between light and shade. In particular, in the case of a projection lens made from resin, the dispersion is large as compared to dispersion from a projection lens made from glass, and accordingly remarkable color bleeding which originates in the chromatic aberration can occur.
In order to improve this color bleeding, conventionally, it has been proposed to provide a diffraction grating (blaze type of diffraction grating) which is designed so as to cancel chromatic aberration, in the projection lens (see International Publication No. WO 2009/028686, for instance).
The dispersion characteristics of a dioptrics element (general projection lens which is used for projector type headlight, for instance) are opposite to those of a diffractive optical element (diffraction grating, for instance). Specifically, the dioptrics element has such characteristics that light of short wavelength (light of wavelength of bluish color) is well refracted and light of long wavelength (light of wavelength of reddish color) is not refracted, but the diffractive optical element has such characteristics on the contrary such that light of long wavelength (light of wavelength of reddish color) is well refracted and light of short wavelength (light of wavelength of bluish color) is not refracted. In addition, the diffractive optical element also has such characteristics such that when a grating period is changed, a direction of diffraction changes, and such that the smaller the grating period is, the larger the amount of diffraction (angle of diffraction) is.
Based on the above described characteristics, a grating shape of the diffraction grating is appropriately designed by using known techniques such as a phase difference function. Thereby, the chromatic aberration of light which is emitted forward through the projection lens can be cancelled, and color bleeding can be reduced which occurs in the vicinity of the boundary line between light and shade in the predetermined light distribution pattern.
Incidentally, in order to improve luminosity (highest luminous-intensity value) in the case of the projector type headlight or the direct projection type headlight, it is effective to enlarge a diameter of the projection lens. Conventionally, a projection lens used for the projector type headlight or the direct projection type headlight has been manufactured from a glass material, but in this case, the weight of the projection lens increases along with the enlargement of the diameter of the lens.
In recent years, in a headlight for vehicles, which uses a semiconductor light emitting element as a light source, there is a tendency to mold the projection lens from resin for the purpose of weight saving, because the temperature of the light source is lowered as compared to the case where a tungsten halogen lamp or a HID electric bulb is used as a light source, and it is also considered to mold the projection lens from resin which is described in the above described International Publication No. WO 2009/028686.